1. Field of the Invention
This invention relates to the field of testing protocols to verify the integrity of double walled tanks.
2. Description of Related Art
Commercial and industrial liquids of all types are stored in storage tanks. One of the most notable such types of storage is for motor vehicle fuel. For reasons of space, many of these tanks are placed underground to be able to supply filling stations and other places where large amounts of liquids are to be stored and distributed. Underground fuel tanks are generally cylindrical in shape and usually have a capacity in the range of 500 to 20,000 gallons or more. Such tanks are generally made of either metal (usually steel) or a fiber reinforced resinous material to resist the often corrosive nature of the materials stored in them.
Storage tanks also are used in a variety of other situations for the storage of liquids. Tanks can be used in industrial settings for the storage of liquids to be used in manufacturing, can be used as storage for end products prior to shipping, or can be used as part of a manufacturing process. Storage tanks are quite ubiquitous and can store all manner of liquids. They are commonly used for the storage of fuels, water, foods, and valuable chemicals, but also can be used to store waste or raw materials. While most of these tanks are in a generally standard size range, they can range from small sizes of less than 100 gallons, to massive tanks the size of small buildings.
Because the liquids stored in such tanks are often hazardous (gasoline for use as a motor fuel being one of the most common), and thus can cause severe environmental damage and greatly impact the lives of people living, working, and recreating in nearby areas, careful attention to the potential for leaks from such tanks must be exercised. In some cases, even small leakage from such an underground tank can have profound effects as the chemical can serve to poison a local water supply, or lead to a situation where nearby soil or other materials become directly hazardous to life. The fact that many of these storage tanks are in areas of higher population density simply exaggerates the problems.
Due to these potential problems from leaks, safer storage tanks have been designed with a double wall, such that a breach in the integrity of either of the inner or outer wall alone will not allow a leak of the liquid contained in the tank outside of the tank. The use of such double-walled tanks (or equivalents thereof, wherein some sort of secondary containment is provided for an otherwise single-walled tank) is increasingly being mandated by government regulation, particularly when such tanks are placed underground or in places where a leak could potentially contaminate soil, air, or water.
While new tanks can be built to more stringent safety standards, because a large number of tanks have already been placed prior to the rules being imposed and the operation for removing and replacing them can be economically unviable, it is often the case that tanks need to be retrofitted in place to comply with more stringent safety regulations or simply taken out of service, which results in a major waste of resources. In one alternative, a tank structure that provides added safety from the hazards of leaking storage tanks comprises the retrofit of a liner which is installed in a single wall tank that has been in use and is already in the ground or in position for use. Certain of these liners can be installed without removing the tank from its original position. Such a lining can be significantly more economical to install as compared with removal and replacement of the single-walled tank with a new double-walled tank.
In one known arrangement for these retrofit liners, a self-supporting bladder is installed into existing storage tanks, particularly into underground storage tanks. Methods of retrofitting tanks in this manner has been described in U.S. patent application Ser. No. 13/161,346 and U.S. patent application Ser. No. 13/252,858, the disclosure of which is entirely incorporated herein by reference. This self-supporting bladder serves as the inner wall, utilizing the existing tank as the outer wall of a double wall system, or can provide a double wall system through the use of an insert placed therein so that the existing tank is unnecessary to provide for double wall protection.
This self-supporting bladder for the creation of a double-walled tank has numerous benefits in the art of underground storage tank systems. While this method provides for a new primary containment system, allowing the existing tank to act as a secondary containment, the new primary containment is not necessarily structurally equivalent to an independent tank. This difference in the structural integrity of the primary containment system renders the known, traditional protocols for testing the integrity of traditional double-walled and single-walled tanks unacceptable and dangerous. The risk of puncturing or rendering the primary containment system of these self-supporting bladders inoperable through these traditional testing techniques is simply too high. These traditional testing protocols simply do not take into account the difference in structural integrity between the primary containment system and the secondary containment system in these self-supporting bladder structures and, as such, is not useable in these types of double-walled structures. Accordingly there is a need in the art for a protocol to test the integrity of a tank that is compatible and reliable with these double-walled tank structures which is able to detect small leaks in the outer wall, inner liner and ullage areas of a tank while also preventing the significant inadvertent damage to the liner caused by traditional testing protocols.